Detergent additives are required in fuels in order to control intake-valve deposits that can cause increased emissions from vehicles. Generally these additives have amine functionality, typically primary or secondary amines or both, and a hydrocarbyl chain that is compatible with the fuel. The amine functionality binds to the intake-valve deposits, and the chain allows solubilization either in the liquid fuel or a carrier fluid that may be included in the detergent control additive package. The amine's base strength and the chain's composition are carefully chosen to provide optimum performance. The importance of controlling intake-valve deposits so that emissions are not increased has led the United States Environmental Protection Agency (EPA) to mandate the use of detergent additives (also known as deposit control additives or DCA's) in all on-road gasoline for use in the United States.
Worldwide concern over the growing shortages of crude oil supplies has promoted the use of many materials as blending agents in gasoline to extend the fuel supply. From the engine or motor vehicle manufacturers' point of view, it seems easiest to employ alcohol blended with gasoline. Methanol, ethanol and butanol have emerged as the most widely used alcohol blending agents. A high level of interest has been shown in the use of “gasohol,” defined herein as a blend of gasoline with from about 5 to about 30 volume percent ethanol, as an automotive fuel. Interest has been especially high in countries such as Brazil which have an intense cultivation of sugar cane, mandioca and other raw materials of vegetable origin adequate for the production of ethanol.
The use of a polar oxygenate such as an alcohol in gasoline blends, however, has far reaching consequences. One of these is the formation of deposits in the fuel induction system such as the carburetor or fuel injector and around the intake valves. These deposits interfere with the efficient operation of the engine and can lead to lower mileage and increased exhaust emissions. It is believed that deposit formation may be caused by several factors. One of these may be the loosening of rust by the alcohol from the walls in pipelines and storage tanks which is then transported through the system until it finds its way into the fuel induction system of the engine.
Another factor may be the presence of trace amounts of acetic acid, acetaldehyde, ethyl acetate and n-butanol in alcohol-gasoline blends which are formed during the production of the alcohol during fermentation. Biofuels such as ethanol and butanols that are made by fermentation processes often contain carbonyl compounds, in particular, aldehydes and ketones, which can react with conventional nitrogen-containing deposit control additives, to form imines or more highly substituted amines by various addition or condensation reactions. For example, fermentation processes can produce acetone, which during purification of the desired alcohol product can form diacetone alcohol, a hydroxyl ketone and its dehydration product, mesityl oxide, an unsaturated ketone. Other ketones and aldehydes can produce corresponding condensation products. These impurities likewise may ultimately end up in the fuel induction system of the engine and contribute to deposit formation. Also the aldehydes and ketones could react with the amine functionality of the detergent additive and reduce its effectiveness. Often the amount of carbonyl compounds present is more than that which would be stoichiometrically required to react with all the amine functionality.
Other factors which may contribute to deposit formation are phase separation which may occur because commercial alcohol has limited solubility in gasoline and the presence of dissolved mineral salts, such as sodium sulfate, which may find their way into the fuel during production, storage and transportation.
Furthermore, alcohol-gasoline blends have different solvency characteristics than non-oxygenated gasoline. This change in solvency can impede the detergent additive performance because the carefully chosen amine base strength and chain composition described previously behaves differently in this medium. In extreme cases of altered compatibility between the detergent additive and the alcohol gasoline blend, the detergent additive can precipitate from solution or insolubilize on the engine's intake valves causing sticking during start-up at cold temperatures.
For enhanced intake-valve keep-clean and clean-up performance recent fuel trends have been to use higher concentrations than the minimum required by the EPA for a particular detergent additive. For example, each detergent additive or deposit control additive, DCA is assigned a “lowest additive concentration” or LAC by the EPA based on its ability to prevent intake-valve deposits as measured by a prescribed test. To meet EPA regulations a one times (1x) treat rate at this concentration level is required. Auto manufacturers, such as General Motors in its Top Tier Program, have recommended the use of higher levels, for example, 2x (or two times) LAC, to provide improved performance of their engines. At high concentrations, low-temperature valve-sticking becomes a critical issue because the high concentration can leave a film of sticky additive on the intake-valve stem causing the valve to remain open during cold-starting. The formation of the sticky film depends on the compatibility of the additive formulation. Good compatibility of an additive formulation corresponds to the formulation being very soluble in fuel (that is, gasoline or alcohol-gasoline blend). However, the change in solvency of alcohol-gasoline blends can upset this compatibility. The concentration and type of the alcohols as well as the additive's composition influence this compatibility. Furthermore, some additive formulations contain a high boiling fluidizer that is very compatible with the additive and that acts to wash the sticky additive off the intake-valve stem.
Thus, there is presently a need for a fuel induction detergent that will either retard or prevent the formation of deposits in the fuel induction system of an internal combustion engine operated on an alcohol-gasoline fuel mixture. Further, it is important that the detergent be effective in very small quantities in order to minimize cost and to avoid adverse effects, such as adding to the gum component of the fuel, increasing combustion chamber deposits, etc. Also it is desirable for the detergent to be immune to the presence of carbonyl compounds and not to cause valve-sticking during start-up at low temperature.
Several detergent compositions have been disclosed. For example, U. S. Pat. No. 4,398,921 discloses a fuel for internal combustion engines comprising from about 70 to about 90 volume percent of hydrocarbons boiling in the gasoline boiling range, from about 5 to about 30 volume percent of ethanol and a detergent amount of a mixture of (1) a mononuclear or dinuclear aromatic hydrocarbon solvent, (2) a hydrocarbyl succinic acid or anhydride corrosion inhibitor (3) a demulsifying agent containing at least one oil-soluble polyether and an oxyalkylated phenol formaldehyde resin, and (4) a Mannich product formed by the reaction between an alkylphenol, an aldehyde and an amine having at least one active hydrogen atom bonded to an amino nitrogen atom.
U. S. Pat. No. 6,652,667 discloses a method for removing engine deposits in a gasoline internal combustion engine by introducing a cleaning composition into a air-intake manifold of a warmed-up and idling gasoline internal combustion engine and running the engine while the cleaning composition is being introduced. The cleaning composition comprises (1) a phenoxy mono- or poly(oxyalkylene) alcohol, (2) at least one solvent selected from an alkoxy mono- or poly(oxyalkylene) alcohol and an aliphalic or aromatic solvent, and (3) at least one nitrogen-containing detergent additive. Useful nitrogen-containing detergent additives include all of the nitrogen-containing compounds that are suitable for use in the formation of the nitrogen-containing detergent compositions of the present invention.
PCT patent application number PCT/EP2006/066623, published as WO 2007/039488 A1, discloses hydroxyalkyl-substituted amino-alkylamides of fatty acids for use as friction modifying agents for fuels such as gasolines containing oxygenated compounds such as ethanol. These amides are formed by reacting a specific class of amines with a carboxylic acid or a carboxylic acid derivative thereof which is capable of reacting with an amine to form an amide. If the resulting amide product contains an active hydrogen atom bonded to an amino nitrogen atom, the amide product is further reacted with an alkylene oxide.
US2007/0094922 A1 discloses compositions which comprise at least one polyalkene amine in a solvent for improving the intake system-cleaning action of fuels which can contain up to 25 percent by volume of oxygen containing materials such as alcohols and ethers. The polyalkene amines employed are those whose polyalkene moiety is the polymerization product of identical or different, straight chain or branched C2 - C6 olefin monomers.
Published U.S. patent application No. US2008/0066377 A1 discloses a biodegradable fuel detergent additive composition for use in gasoline and diesel fuel, including fuels containing alcohols. The detergent additive can be selected from the group consisting of polyamines, polyetheramines, succinimides, succinamides, aliphatic polyamines and Mannich detergents.